Negative active material for non-aqueous rechargeable battery, and non-aqueous rechargeable battery including same

ABSTRACT

The negative active material for a non-aqueous rechargeable battery includes a main component of lithium vanadium oxide, and at least one selected from the group consisting of Li 3 VO 4 , vanadium carbide, and mixtures thereof. The Li 3 VO 4  is included in an amount of 0.5 to 3.0 wt % based on the total weight of the negative active material, and the vanadium carbide is included in amount of 0.5 wt % or less based on the total weight of the negative active material. The negative active material can improve discharge capacity of the non-aqueous rechargeable battery.

CLAIM OF PRIORITY

This application claims priorities to and the benefits of JapanesePatent Application No. 2006-252225 filed in the Japanese IntellectualProperty Office on 19 Sep. 2006, and Korean Patent Application No.2007-0094178 filed in the Korean Intellectual Property Office on the17^(th) of September 2007, the entire contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a negative active material for anon-aqueous rechargeable battery and a non-aqueous rechargeable batteryincluding the same. More particularly, the present invention relates toa negative active material for a non-aqueous rechargeable battery withimproved-discharge capacity, and a non-aqueous rechargeable batteryincluding the same.

2. Description of the Related Art

A conventional non-aqueous rechargeable battery includes a positiveelectrode and a negative electrode being capable of intercalating anddeintercalating lithium ions impregnated in a non-aqueous electrolyte(Japanese Patent laid-open No. 2003-68305, pages 3-11, FIG. 10). Thenegative active material includes lithium vanadium oxide. The lithiumvanadium oxide is prepared by mixing a lithium source, such as lithiumhydroxide and the like, and a vanadium source, such as vanadium trioxideand the like, in a solid-phase method and firing the mixture at 650° C.or higher.

When a non-aqueous rechargeable battery is charged, and its negativeelectrode is electrified to be negative, lithium ions intercalated intothe positive electrode are deintercalated and then intercalated into thenegative electrode.

When a non-aqueous rechargeable battery is discharged, the lithium ionsintercalated into the negative electrode are deintercalated and thenintercalated into the positive electrode.

Accordingly, the non-aqueous rechargeable battery can have a longcycle-life by preventing precipitation of a lithium metal from thenegative electrode.

In general, a non-aqueous rechargeable battery is widely used forportable electronic devices, such as a personal computer, a mobilephone, and the like. The electronic device needs a long operation timefrom full-charge despite huge consumption of electric power.Accordingly, a non-aqueous rechargeable battery with larger dischargecapacity is required.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a negative activematerial for a non-aqueous rechargeable battery being capable ofimproving discharge capacity of the battery.

Another embodiment of the present invention provides a non-aqueousrechargeable battery including the negative active material, and thusshowing excellent discharge capacity characteristics.

According to an embodiment of the present invention, provided is anegative active material for a non-aqueous rechargeable battery thatincludes a main component of lithium vanadium oxide, and at least oneselected from the group consisting of Li₃VO₄, vanadium carbide, andmixtures thereof. The Li₃VO₄ is included in an amount of 0.01 to 5 wt %based on the total weight of the negative active material, and thevanadium carbide is included in an amount of 0.5 wt % or less of thetotal weight of the negative active material.

The negative active material can be prepared by adding at least oneselected from the group consisting of Li₃VO₄, vanadium carbide, andmixtures thereof to a mixture of a lithium source material and avanadium source material, and then subjecting the resulting mixture tofiring under an inert atmosphere, such as nitrogen, argon, and so on.

The negative active material may include vanadium carbide in an amountof 0.5 wt % or less.

The negative active material for a non-aqueous rechargeable battery hasan average particle diameter ranging from 5 to 50 μm.

According to another embodiment of the present invention, provided is anegative active material for a non-aqueous rechargeable battery thatincludes a main component of lithium vanadium oxide and vanadium carbidein an amount of 0.5 wt % or less.

According to a further embodiment of the present invention, provided isa non-aqueous rechargeable battery that includes a negative electrodeincluding the negative active material, a positive electrode, and anelectrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings in which likereference symbols indicate the same or similar components, wherein:

FIG. 1 is a vertical cross-sectional view of a non-aqueous rechargeablebattery according to one embodiment of the present invention.

FIG. 2A is a graph showing the relationship between Li₃VO₄ content andaverage particle diameter of the negative active material in thenegative active mass for a non-aqueous rechargeable battery according toExample 1.

FIG. 2B is a graph showing the relationship between Li₃VO₄ content ofthe negative active material in the negative active mass for anon-aqueous rechargeable battery according to Example 1 and dischargecapacity.

FIG. 3 is a graph showing vanadium carbide content of the negativeactive material in the negative active mass for a non-aqueousrechargeable battery according to Example 6, discharge capacity, anddischarge capacity maintenance ratio at high rate.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a vertical cross-sectional view of a non-aqueous rechargeablebattery according to one embodiment of the present invention.

Referring to FIG. 1, a non-aqueous rechargeable battery 1 according toone embodiment of the present invention is fabricated as a spiralcylindrical lithium rechargeable battery. The non-aqueous rechargeablebattery 1 includes a center pin 6 and an electrode assembly 10 woundaround the center pin 6. Herein, the electrode assembly 10 includes apositive electrode 3 and a negative electrode 4, and a separator 5inserted therebetween. Accordingly, the electrode assembly 10 has acylindrical structure.

The positive electrode 3 is formed by disposing a positive electrodeactive mass 3 a including a positive active material on both surfaces ofa positive electrode current collector 3 b. The negative electrode 4 isformed by disposing a negative active mass 4 a including a negativeactive material on both surfaces of a negative electrode currentcollector 4 b. The cylindrical electrode assembly 10 is housed in acylindrical case 2 with a hollow space and impregnated with anelectrolyte (not shown). The positive electrode 3 contacts with the case2 and also has a positive terminal 7 protruded at the bottom.

The electrode assembly 10 is mounted with insulating plates 9 b and 9 aat the top and bottom. The positive electrode current collector 3 bpasses through the insulating plate 9 a and contacts with the positiveterminal 7 by a positive electrode lead 11. A safety plate 13 is mountedabove the insulating plate 9 b located at the opening of the case 2 inthe same direction as the insulating plate 9 b. A negative terminal 8shaped as a convex cap in the opposite direction to the safety plate 13,is mounted on the safety plate 13. The negative electrode currentcollector 4 b passes through the insulating plate 9 b and contacts withthe negative terminal 8 by a negative electrode lead 12. In addition,the safety plate 13 and the edge of the negative terminal 8 are sealedby a gasket 14, which separates them from the positive terminal 7.

The positive active material and the electrolyte may include a commonpositive electrode and electrolyte for a non-aqueous rechargeablebattery. For example, the positive active material may include a lithiumtransition element oxide such as lithium cobalt oxide and the like. Inaddition, the electrolyte may include a solute including a lithium saltconsisting of LiPF₆, Li₂SiF₆, Li₂TiF₆, LiBF₄, and the like in a solventsuch as ethylene carbonate, diethyl carbonate, or the like.

The negative electrode 4 includes a negative active material including alithium vanadium oxide as a main component. It is formed by mixing 80 wt% of the negative active material, 10 wt % of acetylene black, 10 wt %of a binder, coating the mixture on, a copper current collector, andpressing the coating to have a mass density of 1.8 g/cm³.

According to one embodiment of the present invention, the negativeactive material may be selected from the group consisting of Li₃VO₄,vanadium carbide (VC), and mixtures thereof, which are commonlyconsidered as impurities.

The Li₃VO₄ has a lower melting point of about 600° C. than lithiumvanadium oxide (LiVO₂) as a main component. Accordingly, when a negativeactive material is prepared through firing, the firing can promotecombination of LiVO₂ particles as a main component. In addition, as theLi₃VO₄ is increasingly included, a negative active material may have abigger average particle diameter.

The Li₃VO₄ may be included in an amount of 0.01 to 5 wt % based on thetotal weight of the negative active material. According to oneembodiment of the present invention, it may be included in an amount of0.5 to 3 wt %, while according to another embodiment of the presentinvention, it may be included in an amount of 1 to 2 wt %. When it isincluded out of the above range, it may deteriorate discharge capacity.

In addition, the negative active material including Li₃VO₄ may have anaverage particle diameter ranging from 5 μm to 50 μm. In one embodiment,it may have an average particle diameter ranging from 10 μm to 50 μm,and in another embodiment, it may have an average particle diameterranging from 10 μm to 40 μm.

When a negative active material with a smaller average particle diameterthan the above range is mixed with a conductive agent, it may have lesspossibility of contacting with the conductive agent.

In addition, when a negative active material is prepared to increasinglyinclude Li₃VO₄, it may have a bigger average particle diameter butdeteriorate discharge capacity. The Li₃VO₄ is considered as an impurityin the negative active material.

On the other hand, when a negative active material includes VC, which isa good conductive agent with a volume resistance rate of 150×10−6 Ω·cm,it may have increased conductivity inside a particle. For example, thenegative active material can resist against a high efficiency dischargeof 3 mA/cm². However, VC can excessively take vanadium from a lithiumvanadium oxide playing a role of intercalating lithium, and therebydeteriorate discharge capacity. Accordingly, VC may be included in anamount of 0.5 wt % or less based on the total weight of the negativeactive material. In one embodiment, it may be included in an amount of0.01 to 0.4 wt % according to another embodiment of the presentinvention. When a negative active material includes VC out of the aboverange, it may have deteriorated discharge capacity.

On the other hand, a negative active material with the aforementionedcomposition can be prepared by preparing a mixture of a lithium sourcematerial and a vanadium source material, adding a material selected fromthe group consisting of Li₃VO₄, vanadium carbide, and mixtures thereofthereto, and firing the resulting product under an inert atmosphere suchas nitrogen, argon, and the like.

Also, a negative active material including Li₃VO₄ as an impurity can beprepared by using lithium in an excess of amount to the vanadium.Therefore, without adding Li₃VO₄, a negative active material includingLi₃VO₄ can be prepared by preparing a mixture of a lithium sourcematerial and a vanadium source material in amounts having a mole ratioof Li:V=1.13:0.9 or more. In one embodiment, concerning the amount ofLi₃VO₄ included in the negative active material, the mole ratio of Li:Vmay be from 1.13:0.9 to 1.21:0.9.

A negative active material including VC as an impurity also can beprepared by using vanadium in an excess of amount to the lithium.Therefore, without adding VC, a negative active material including VCcan be prepared by preparing a mixture of a lithium source material anda vanadium source material in amounts having a mole ratio of Li:V=morethan 1.08:0.9 or less than 1.13:0.9, concerning the amount of Li₃VO₄included in the negative active material.

The lithium source material may include lithium hydroxide and the like,and the vanadium source material may include vanadium oxide such asV₂O₃.

The lithium source material and vanadium source material can be mixed invarious ratios considering the amount of lithium and vanadium includedin a negative active material as a final material.

Then, a material selected from the group consisting of Li₃VO₄, vanadiumcarbide, and a mixture thereof is added to the above mixture in the sameratio as aforementioned. The resulting mixture is fired under an inertatmosphere.

The firing can be performed at a temperature of from approximately 1100°C. to 1200° C.

The following examples illustrate the present invention in more detail.However, it is understood that the present invention is not limited bythese examples.

EXAMPLE 1

A negative active material was prepared in the following method, andthen measured regarding discharge capacity and average particle diameterdepending on the content of Li₃VO₄ therein to evaluate the relationshipof the content of Li₃VO₄ to discharge capacity and average particlediameter thereof. The results are shown in FIGS. 2A and 2B.

Preparation of a Negative Active Material

LiOH (lithium hydroxide) and V₂O₃ (vanadium trioxide) were mixed in amole ratio of 1.22:1 between lithium and vanadium, and Li₃VO₄ wasrespectively added thereto in an amount of 0 wt %, 1 wt %, 2 wt %, 3 wt%, and 5.5 wt %. The resulting product was fired at 1100° C. under anitrogen atmosphere to prepare a negative active material includingLiVO₂ as a main component and Li₃VO₄.

1-2) Evaluation

The negative active material according to Example 1 was measuredregarding average particle diameter. Then, an X-ray diffraction methodwas employed to measure the content of Li₃VO₄ in the negative activematerial, and a laser diffraction method was employed to measure anaverage particle diameter thereof. The results are shown in FIG. 2A.

The X-ray diffraction analysis was performed at a scanning speed of0.02°/sec in a range of 2θ of 10-80° by using X-rays of CuKa (1.5418 Å,40 kV/30 mA). The data obtained by X-ray diffraction analysis was fittedby the Rietveld method to calculate the amount of Li₃VO₄, and when theamount of Li₃VO₄ was calculated, the Cerius2 program was used.

FIG. 2A is a graph showing the relationship of Li₃VO₄ content in thenegative active material to an average particle diameter thereof.Referring to FIG. 2A, the vertical axis in the graph indicates averageparticle diameter (unit:μm), while the horizontal axis is Li₃VO₄ content(unit:wt %).

As shown in FIG. 2A, the higher the content of Li₃VO₄ included in thenegative active material, the larger the average particle diameter ofthe negative active material.

Then, the negative active material according to Example 1 was evaluatedregarding improvement of discharge capacity.

The discharge capacity evaluation was performed by using the samespecimens as a negative electrode 4. In other words, a negativeelectrode was prepared by mixing 80 wt % of a negative active materialincluding lithium vanadium oxide, 10 wt % of acetylene black, and 10 wt% of a binder, coating the mixture on a copper current collector, andthen pressing to have a mass density of 1.8 g/cm³.

Then, a test cell of standard open-circuit potential was fabricated bydisposing metal lithium at the negative electrode and a specimen at apositive electrode, and then measured regarding discharge capacity witha current density of 0.5 mA/cm². The results are shown in FIG. 2B.

In FIG. 2B, the vertical axis in the graph indicates discharge capacity(no unit), and the horizontal axis therein indicates Li₃VO₄ content(unit: wt %).

The discharge capacity was measured as a ratio calculated by adjustingdischarge capacity to be 100, when Li₃VO₄ is included in an amount of 0(hereinafter, referred to as Comparative Example 1). In addition, A1 inFIG. 2 indicates discharge capacity and B1 indicates average particlediameter.

As shown in FIG. 2B, the higher the content of Li₃VO₄ included in thenegative active material, the more the discharge capacity was increased.However, when it was included in an amount of more than 3.0 wt %, itsignificantly decreased discharge capacity. The reason was the same asaforementioned.

Referring to FIGS. 2A and 2B, there are four examples of differenceweight percentage of Li₃VO₄ included in the negative active material andthe corresponding average particle diameter ranging:

EXAMPLE 2

A negative active material including lithium vanadium oxide as a maincomponent was prepared to include Li₃VO₄ in an amount of 0.5 to 3.0 wt%, and thereby to have an appropriate average particle diameter. Whenthe negative active material was used for the negative electrode, it canimprove discharge capacity by 30 to 40% compared with a non-aqueousrechargeable battery not including Li₃VO₄ in the negative activematerial. Herein, the negative active material had an average particlediameter ranging from 10 to 50 μm.

EXAMPLE 3

The negative active material including lithium vanadium oxide as a maincomponent was prepared to include Li₃VO₄ in an amount of 1 to 2 wt %,and thereby to have an appropriate average particle diameter. When thenegative active material was used for the negative electrode, it canimprove discharge capacity by 40% compared with a non-aqueousrechargeable battery not including Li₃VO₄ in the negative activematerial.

EXAMPLE 4

The negative active material including lithium vanadium oxide as a maincomponent was prepared to include Li₃VO₄ in an amount of 1 to 2 wt %,and thereby to have an appropriate average particle diameter. When thenegative active material was used for the negative electrode, it canimprove discharge capacity by 40% compared with a non-aqueousrechargeable battery not including Li₃VO₄ in the negative activematerial. Herein, the negative active material had an average particlediameter ranging from 20 to 33 μm.

EXAMPLE 5

The negative active material including lithium vanadium oxide as a maincomponent was prepared to include Li₃VO₄ in an amount of 0.5 to 2.3 wt%, and thereby to have an appropriate average particle diameter. Whenthe negative active material was used for the negative electrode, it canimprove discharge capacity by 40% compared with a non-aqueousrechargeable battery not including Li₃VO₄ in the negative activematerial. Herein, the negative active material had an average particlediameter ranging from 10 to 40 μm.

EXAMPLE 6

A negative active material was prepared in the following method, andthen measured regarding discharge capacity and discharge maintenancerate at a high rate depending on VC content therein. The results areshown in FIG. 3.

2-1) Preparation of a Negative Active Material

A negative active material was prepared not including Li₃VO₄, but havingvarious amounts of VC.

First of all, LiOH (lithium hydroxide) and V₂O₃ (vanadium trioxide) weremixed in a mole ratio of 1.22:1 between lithium and vanadium, and then,VC was respectively added thereto in the various amounts shown in FIG.3. The resulting products were fired at 1100° C. for 10 hours under anitrogen atmosphere.

In addition, the negative active material was ground with a jet mill tohave an average particle diameter of about 7 μm in order to removeinfluences of the average particle diameter.

2-2) Evaluation

The negative active material according to Example 6 was measuredregarding VC content and average particle diameter in the same method asExample 1.

In addition, it was evaluated regarding discharge capacity and dischargemaintenance rate at a high rate depending on VC content. The results areshown in FIG. 3.

Herein, a specimen and a test cell for measurement of discharge capacityand discharge maintenance rate at a high rate were formed according tothe same method as in the negative active material of Example 1.

The discharge capacity was measured with 0.5 mA/cm² of a current densityin the test cell, and then as a ratio calculated by adjusting dischargecapacity to be 100 when VC content was included in an amount of 0(hereinafter, referred to as Comparative Example 2).

In addition, the high-rate discharge maintenance rate was measured as aratio of discharge capacity measured with a current density of 3 mA/cm²(hereinafter, referred to as a high rate discharge capacity), whendischarge capacity measured with 0.5 mA/cm² of a current density in thetest cell (hereinafter, referred to as low-rate discharge capacity) wasadjusted to be 100.

FIG. 3 is a graph showing the relationship of VC content in the negativeactive material to discharge capacity, average particle diameter andhigh-rate discharge maintenance rate.

In FIG. 3, the horizontal axis in the graph indicates VC content (unit:wt %), while the vertical axes respectively indicate discharge capacity(no unit) and high-rate discharge maintenance rate (no unit). Inaddition, A2 is discharge capacity, B2 is average particle diameter ofthe negative active material (unit:μm), and C2 is high-rate dischargemaintenance rate.

As shown in FIG. 3, the negative active material had high dischargecapacity when it included VC in an amount of 0.5 wt % or less. On thecontrary, it had sharply deteriorated discharge capacity when itincluded VC in an amount of 0.5 wt % or more. In addition, it had animproved high-rate discharge maintenance rate in proportion to theamount of VC. Since the VC has a low volume resistance rate asaforementioned, it can improve conductivity inside a particle when moreVC is included.

Accordingly, since a negative active material including lithium vanadiumoxide as a main component was prepared to include 0.5 wt % of VC, it canimprove discharge capacity and high-rate discharge maintenance rate.

EXAMPLE 7

LiOH (lithium hydroxide) and V₂O₃ (vanadium trioxide) were mixed in amole ratio of 1.21:0.9 between lithium and vanadium. The resultingmixture was fired at 1100° C. under a nitrogen atmosphere for 10 hoursto prepare a negative active material including LiVO₂ as a maincomponent and 5 wt % of Li₃VO₄.

EXAMPLE 8

LiOH (lithium hydroxide) and V₂O₃ (vanadium trioxide) were mixed in amole ratio of 1.22:1 between lithium and vanadium, and Li₃VO₄ and VCwere respectively added thereto in an amount of 1 wt % and 0.05 wt %.The resulting product was fired under a nitrogen atmosphere at 1100° C.for 10 to prepare a negative active material including LiVO₂ as a maincomponent, 1 wt % of Li₃VO₄, and 0.05 wt % of VC.

According to the embodiment of the present invention, a negative activematerial can improve discharge capacity when it is applied to anon-aqueous rechargeable battery such as a lithium ion rechargeablebattery and the like.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A negative active material for a non-aqueous rechargeable batterycomprising: a main component of lithium vanadium oxide; and anothercomponent at least one selected from the group consisting of Li₃VO₄,vanadium carbide, and mixtures thereof, with the Li₃VO₄ is included inan amount of 0.01 to 5 wt % based on the total weight of the negativeactive material, and the vanadium carbide is included in amount of 0.5wt % or less based on the total weight of the negative active material.2. The negative active material of claim 1, wherein the Li₃VO₄ isincluded in an amount of 0.5 to 3.0 wt % based on the total weight ofthe negative active material.
 3. The negative active material of claim1, wherein the vanadium carbide is included in an amount of 0.01 to 0.4wt % based on the total weight of the negative active material.
 4. Thenegative active material of claim 1, wherein the negative activematerial has an average particle diameter ranging from 5 to 50 μm.
 5. Anon-aqueous rechargeable battery comprising: a negative electrodecomprising a negative active material with a main component of lithiumvanadium oxide and another component at least one selected from Li₃VO₄,vanadium carbide, and mixtures thereof; a positive electrode; and anelectrolyte, the Li₃VO₄ is included in an amount of 0.01 to 5 wt % basedon the total weight of the negative active material, and the vanadiumcarbide is included in amount of 0.5 wt % or less based on the totalweight of the negative active material.
 6. The non-aqueous rechargeablebattery of claim 5, wherein the Li₃VO₄ is included in an amount of 0.5to 3 wt % based on the total weight of the negative active material. 7.The non-aqueous rechargeable battery of claim 5, wherein the vanadiumcarbide is included in an amount of 0.01 to 0.4 wt % based on the totalweight of the negative active material.
 8. The non-aqueous rechargeablebattery of claim 5, wherein the negative active material has an averageparticle diameter ranging from 5 to 50 μm.